blank wrote:

Tank is 75 gal freshwater community setup
Lighting is 3 x 30w T8 fluro tubes (Actinic blue, ColorMax and plain
white).

As others have noted, the lighting is a bit low.

I realise lighting is low, but cant do much about it because
the hood is pre-formed plastic to suit the tank (once piece of glass
with rounded corners).

Any chance of replacing the existing bulbs with Compact Flourescents?
They'll put out a lot more light in the same space.

I see a couple of other people have suggested that you need CO2, and it
would certainly help. However, providing CO2 on a 75 gallon tank is not
a trivial task. And, you may not really need it. I was using CO2 on my
heavily planted 20 gallong for awhile, and it worked really well. But I
got tired of replacing the yeast solution and just stopped using CO2,
and my plants many months later are doing just fine.

Something you might consider is trying different kinds of plants. I've
got about 8 species of plant in my tank, but I've tried at least twice
that many. You may find a variety that does really well in your tank.

--
Eric Schreiber
www.ericschreiber.com